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I am taking screen captures of an OpenGL application in real-time using glReadPixels() and experiencing a performance issue. I've followed the advice provided here:http://www.gamedev.n...g-glreadpixels/

This works great on a Windows 7 system with AMD FirePro M5950 graphics and a very old Ubuntu 12.04 system with Radeon RV250 [Mobility FireGL 9000] graphics, but chokes on new Ubuntu 12.04 system with integrated Intel graphics. glReadPixels() takes >600ms to return even though (as I understand it) it should return immediately due to the asynchronous PBO use. I'm using GLEW for the OpenGL extensions and it appears that the graphics drivers support the GL_ARB_pixel_buffer_object extension. Any ideas? somoth mentioned that supplying wrong PBO flags can cause stalls, but i don't know what those might be.

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"but chokes on new Ubuntu 12.04 system with integrated Intel graphics"
Maybe i'm jaded, but whenever i encounter the words intel and integrated, I move on, and never look back

they aren't very strong GPUs, they're full of driver issues and implementation variances.. sometimes it will outright lie to you (glGet*)
however! Newer intel integrated chips have orders of magnitude better openGL support! all the way up to 4.1 from what ive read!
So, personally, I will be waiting until "a larger percentage" of my potential audience has newer intel chips, and continue to pretend the older ones never existed

This post is only a warning, that if you really want to support the older intel integrated chips, you are in for a potential nightmare...
I'm sure there are plenty of people who can help you, since many if not most people who aren't making hobbyist games, will choose to include the widest audience possible =)

edit: to actually be helpful,
what happens when you supply an opengl implementation with something it doesn't support may cause it to run it in software mode
which is many orders of magnitude slower than hardware accelerated paths =)
for example, i imagine that if you tried GL_RGBA16 or GL_RGBA16F, it would do it all on the cpu
it may also not support RGB8, but i can't answer concretely what it can and can't do, and i'm unsure if you can ask the driver whether or not it's emulating it or not =)

http://www.opengl.org/wiki/Common_Mistakes#Texture_upload_and_pixel_reads
note that using GL_RGBA is not a "real format" because it doesn't describe internal precision, using GL_RGBA8 was determined to be the fastest.. i was unable to find any information for intel cardsEdited December 7, 2012 by Kaptein

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I would double check your format of your PBO and make sure that it matches the frame buffer that you're reading from. I've noticed significant performance hits if openGL needs to convert from the framebuffer's format to the PBO's format. Sometimes when you request a framebuffer format, you don't always get what you asked for.

Cheers,

Bob

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Maybe i'm jaded, but whenever i encounter the words intel and integrated, I move on, and never look back

I have to agree with you, the intel graphics have been a real thorn in my side. Unfortunately i'm stuck with them. I tried changing the GL_PACK/UNPACK_ALIGNMENT? and different formats (e.g. GL_RGBA8), but still no luck.

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You use Unpack whenever you are sending information to the Card. You use Pack whenever you want to read something from the card. One of the way you can speed it up is to have two FBOs. That way wile you are saving one FBO you can start writing to the one at the same time.

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Good Evening,
I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
I am really stucked right now because of the fundamental question:
Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on.
In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
Should I treat those debug objects as entities/components?
For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
Regards,
LifeArtist

Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
Let's go:
Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
There were several more but i forgot/solved them at time of writing
Thanks in advance

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